Owing to the ever increasing use of digital electronic circuits, and the various control options made possible by the availability of such circuits, it is becoming increasingly necessary to provide suitable transducers that operate in the digital domain. For example, induction resolvers have long been used in industry for translating mechanical angular position into a responsive analog signal. The analog signal is typically a phase encoded sine-wave signal produced by transformer action in one or more coils of the resolver. Such resolvers are capable of high resolution of angular position. However, the resultant phase encoded sine-wave signal is unsuitable for direct use in digital circuits. Therefore, some form of phase-to-digital conversion has necessarily been employed.
One example of a phase-to-duty cycle conversion apparatus is disclosed in U.S. Pat. No. 3,639,850, issued Feb. 1, 1972, to Herman H. Brooks. Brooks discloses circuitry for squaring the phase encoded sine-wave signal delivered from a conventional resolver, comparing the squared signal with a similarly squared reference signal, and responsively producing a duty cycle signal. Similar circuitry is shown in a subsequent patent, U.S. Pat. No. 3,828,331, also issued to Brooks on Aug. 6, 1974.
While both of these patents do disclose the provision of a duty cycle signal responsive to the angular position of a resolver, they, in accord with other known art, suffer the disadvantage of requiring that the resolver be excited with sine-wave signals. As those skilled in the art are aware, the generation of precision sine-wave signals is relatively complicated. The situation is further complicated when a resolver having multiple stator coils, each requiring a phase shifted excitation signal, is employed. In the case of a dual stator resolver, both sine and cosine excitation signals must be produced. The circuitry required merely to produce the excitation signals is complex and expensive, as is the circuitry subsequently required for decoding or demodulating the signals.
The present invention is directed to overcoming one or more of the problems as set forth above.